This invention relates generally to a method for determining a change in direction of rotation of a motor.
In window regulators, it is important to be able to detect the presence of an obstruction when a window is closed, in particular to avoid pinching the obstruction. A system for detecting an obstruction interrupts a window drive when an obstruction is detected. It is also important to know a position of the window in an opening in order to switch off the obstruction detection system before the window enters a roof seal. Otherwise, the obstruction detection system regards the roof seal as an obstruction and interrupts the window drive before the window is fully lodged in the roof seal.
Devices to detect the position of the window in the opening use a sensor that triggers an incremental counter, allowing an angular position of the motor to be known. For example, a Hall effect sensor is used to detect a change of polarity of a magnetic ring mounted on a motor shaft. A drawback is that a single sensor does not allow for a change in the direction of rotation of the motor to be detected so that an incremental counter triggered by the sensor is inaccurate and does not allow for the position of the motor to be known with certainty. Therefore, the position of the window is not known accurately either.
To solve this problem, other devices to detect the position of the window in the opening use two sensors facing a ring with alternating polarity. The sensors are located near the motor and offset at an angle in such a way that the direction of the motor is deduced from the sensor state sequence. The incremental counter then takes into account the direction of rotation of the motor. The drawback is that these systems are more bulky and more expensive.
All these devices also have other drawbacks. In particular, the frequency of detection of the polarity of the ring on the motor by the sensor(s) depends on the rotating speed of the motor. When the rotating speed of the motor decreases, the frequency and quality of detection by the sensor(s) decreases. Knowledge of the position of the motor and of the window then becomes less accurate.
Moreover, when an obstruction is detected, the motor is immediately instructed to reverse its direction of rotation to lower the window and reduce pinching. However, the drive motor has a degree of inertia which prevents the direction of rotation of the motor from being reversed immediately. The time lapse between a motor reverse command and actual reversal of the motor is prejudicial to knowledge of the motor position.
In addition, when a command is sent to the motor to stop, it does not do so immediately due to its inertia. A slight reverse rotation movement may even occur, as transmission of the movement is not completely irreversible.
A need therefore exists to determine accurately the change of direction of rotation of a motor.